Understanding and improving people’s judgments of synergistic risks

Abstract

Certain hazard combinations present a risk that is greater than the sum of the risk attributable to each constituent hazard. These ‘synergistic risks’ occur in several domains, can vary in magnitude, and often have life-threatening consequences. However, research concerning the extent to which people understand synergistic risks is in its infancy, and extant studies investigating this topic have encountered problems in identifying valid measures of subjective risk judgments for combined hazards. Consequently, few firm conclusions can be made about the extent to which people understand synergistic risks.
This thesis presents four original research papers that aim to provide greater insight into peoples’ judgments of synergistic risks, and investigates how such judgments may be assessed and improved. Each of the studies presented in the four papers employs data obtained via questionnaires specifically designed to address each research question. In the first paper, two studies are presented that examine whether people believe that combined hazards can present synergistic risks. In the second paper, qualitative data is analysed to explore the cognitive reasoning that individuals employ when assessing the risk for combined hazards. The third paper presents a study that assess a new metric for the assessment of risk judgments for combined hazards, and a second study in which domain-experts’ and non-experts’ judgments are compared. The final paper features a study that investigates which message content (i.e., antecedent vs. probabilistic data) most effectively informs people about synergistic risks.
The results show that many people can make veridical judgments of synergistic risks. The findings indicate such judgments may depend on factors that include hazard-specific knowledge, judgmental experience and a rudimentary awareness of an
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underlying causal mechanism for the increased risk. However, many people also make non/less veridical judgments; often underestimating the magnitude of the synergistic risk or employing an additive risk model which corresponds to the notion of ‘adding’ one hazard to another. Furthermore, the findings suggest risk judgments for combined hazards do not vary according to hazard domain but, rather, according to the hazard characteristics. Importantly, the research also identifies both (a) a valid method of assessing peoples’ risk judgments for combined hazards, and (b) risk communications contents that can lead to significant improvement in individuals’ understanding of synergistic risks

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ORCID for Ian G.J Dawson: orcid.org/0000-0003-0555-9682

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